Apparatus for cooling compressed gases



1 NW. 3, was.

Filed Dec. 22, 1945 v M. H. OLSTAD. ET AL APPARATUS FOR COOLINGCOMPRESSED GASES 2 Sheets-Sheet 1 INVENTOR Patented Nov; 30, 1948UNl'lED STATES PATENT OFFICE Martin H. Olstad, Port Washington, andAllan E. Williams, White Plains, N. Y., assignors to Niagara BlowerCompany, Buffalo, N. Y.,- a-corporation of New York Application December22, 1943, Serial No. 515,310

16 Claims. (Cl. 62-2) This invention relates to a heat exchanger forcooling compressed'gases and more particularly to the use of anevaporative type of heat exchanger to effect the cooling of compressedair, or othcrgas having a component which liquefles on cooling thecompressed gas, and to provide compressed air having a reduced moisturecontent, the practice of the invention being particularly advantageouswhen air is being compressed for use in driving equipment havingrotating parts or for use in paint spraying, metallic shot blastequipment, or where freezing .ionditions are encountered where thepresence of water is especially harmful.

' When gases are compressed heat is developed which is removed bysupplying cooling water to the jackets surrounding 'the compressor orsurrounding an intercooler or an aftercooler through which thecompressed gas is passed between and following, respectively, theseveral compression As new practiced, surface water taken stages. fromnearby lakes and streams is used for this purpose since surface water isa readily available source of cooling medium.

However, in most localities of the United States, during the warm monthswhen cooling is particularly needed, the temperature of this surfacewater exceeds the average wet bulb temperature by ten or more degrees.When this surface water is passed through a shell, and tube cooler tocool the cooling water being recirculated through the Jacket of thecompressor and its inter or aftercoolers, this cooling water can becooled to approximately F. of the surface water. In accordance with thepresent invention it has been found that by subjecting this coolingwater of the compressor in a closed circuit to evaporative cool-' ing,this cooling water can be cooled to less than 10 F. of the wet bulbtemperature of the outside I air. Since the wet bulb temperature is 10F.

lower than the temperature of the surface water available, it will beseen that the cooling water cooled by evaporative cooling in accordancewith the present invention is much colder than cooling water cooled bysurface water as now practiced. Consequently the cooling water suppliedin accordance with the present invention isv much colder than whencooled by the surface water available and the compressed air is cooledto a lower temperature and as the compressed air leaves the aftercoolerat its dewpoint it will be seen that compressed air cooled in accordancewith the present invention contains much less water than iii compressedair cooled conventionally with surface water.

It has further been found that in the practice of the invention thecompressed gas can be passed directly through the coil which isexternally subjected to the evaporative cooling effect of streams of airand water. gases directly, the gases can be cooled closer to the wetbulb temperature of the outside air than by indirect cooling as by waterwhich is cooled and then used to cool the gases. Accordingly, animportant feature ofthe invention resides in the direct cooling ofcompressed gases by evaporative cooling.

By actual test cooling compressed air by evaporative cooling in a closedcircuit in accordance with the present invention provides a leavingtemperature of the compressed-air which is from 10 to F. cooler than canbe obtained by the use of surface water during the warm months whencooling is needed and provides compressed air that contains fromone-half to three-fourths the amount of water formerly experienced withthe best practice using surface water. Thereduction of the water contentof the compressed air or other gases by the practice of the presentinvention is a particularly important feature as the use of drier airprevents water damage to pneumatic equipment operated by the compressedair. Thus, particularly with pneumatic equipment or tools containingrotating parts, water in the compressed air supplled to the equipmentwashes out the lubricant and causes rapid wear of the rotating parts.Further, with pneumatic paint sprayers, the presence of water in thecompressed air causes the paint to blister. Water in the compressed airalso tends to freeze on release from pneumatic tools thereby freezing upthe pneumatic tool and halting production. The moisture of compressedair also rusts metallic shot in blast cleaning equipment. With manygases, a low water content is desirable, as in illuminating gas wherethe water content must be held to a maximum fixed by the authorities andwhich has reduced heating value and is liable to freeze in ports whenthe water content is too high and also in \many chemical industries, aswith butane gas in the manufacture of synthetic rubber, where low watercontent is important. In short, the moisture in compressed air or othergases is highly detrimental and cooling the compressed air to reduce itswater content is highly desirable.

Accordingly, it is one of the principal objects of Byso cooling thecompressed to a lower temperature and contains a substantially reducedamount of water as compared with surface water cooling equipment.

Another object of the invention is to provide a heat exchanger forcooling compressed gases wherein the evaporative cooling of thecompressed gases is effected directly. instead of indirectly as throughwater which i cooled and then used to cool the gases, this permitting ofcooling the gases closer to the wet bulb temperature or the outside air.

Another important object of the present invention is to provide a simpleand efficient apparatus for cooling a plurality of streams of thecooling water or the compressed gases from a compressor and in which thecooling efl'ect is obtained from the evaporation of water in a stream ofatmospheric air, thereby to greatly reduce the amount of cooling waternecessary for the operation of the apparatus;

Another object of the invention is to provide such apparatus in whichthe several streams of the cooling water or the compressed gas from anystage of the compressor is cooled in the same spray chamber, thereby toprovide a single unit for cooling all of the streams.

Another object of the invention is to provide an apparatus for feedingthe washed air discharged from the spray chamber into the air inlet ofan air compressor when the temperature of this air is below thetemperature of the outside air, there.- by to increase the efliciency ofthe compressor since it is supplied with cooler .and heavier air,

and also washing the air supplied to the compressor and maintaining amore constant condition of the air supplied to the compressor.

Other objects are to provide such apparatus which is simple andinexpensive in construction and which will stand up under conditions ofsevere and constant use without getting out of order or requiringrepairs.

In the accompanying drawings:

Fig. l is a diagrammatic representation of a two stage air compressor inwhich the air from both stages is cooled in an evaporative type heatexchanger embodying the invention.

Fig. 2 is a vertical central section through the evaporative type ofheat exchanger shown in Fig. 1.

Fig. 3 is a view similar to Fig. 1 showing a two stage air compressor inwhich both the cooling water and also the compressed air is cooled in anevaporative type heat exchanger embodying Y the present invention.

Fig. 4 isa further modification of the invention in which air from bothstages of a two stage air compressorand also the cooling water arecooled in an evaporative heat exchanger embodying the present invention.

While the invention is illustrated as used in connection with aircompressors. it will be understood that features of the invention canalso be applied to any type of gas compressor where cooling of thecompressed gas is advantageous, as previously indicated,-particularlywhere the gas has a component which liqueiies on cooling the compressedgas.

In the form of the invention shown in Figs. 1 and 2 the numeral 5represents an air compressor having a low pressure cylinder I which issupplied with air from a duct l and the air from which leaves through aduct I. The compressor is also shown as having a high pressure cylinderit, the air to which is supplied from a duct II and the compressed airfrom which passes ranged through a duct i2. Each cylinder 8, i issuitably jacketed and a stream of cooling water is circulated throughthese Jackets through jacket water connections l3. Both the high and lowpressure stages of air are cooled in an evaporative type of coolerembodying the present invention, this being shown as comprising a sheetmetal casing l which is mounted on a tank i8 forming the base of thecasing, this tank It containing a body of water H which is evaporated toprovide the cooling effect. The water ii is pumped in any suit-' ablemanner to piping I8 arranged in the upper part of the spray chamber,this piping carrying a series of nozzles itthrough which the water isdischarged over two banks of coils A and B which are in the form ofseparate coils and can be of any suitable construction. A fan housing isshown as mounted in the'upper part of the casing IS, the inlets of thisfan housing being in communication with the interior of the casing i'5so as to exhaust air therefrom. A fan wheel 2| is shown as arrangedwithin the fan housing 20 and as fast to a fan shaft 22 which can beiournaled on the casing i5 and driven in any suitable manner. The fanhousing is shown as provided with a horizontal outlet 23 whichcommunicates with an exhaust duct 24. The outlet 28 of the fan housing20 also communicates with a vertical bypass duct 25, the lower end ofwhich connects with a horizontal air inlet duct 28 which communicateswith the interior of the casing i 5 below the coils A and B, asindicated at 28.

The discharge 23 of the fan housing is also shown as communicating witha vertical duct 30, the lower end 3| of which is open to the atmosphereand this duct 30 alsoconnecting with the duct 1 to the air compressor soas to supply the air thereto.

In the form of the invention shown in Fig. 1, the ducts 8 and l iconnect with the bank of cooling coils A so that the first stage of airfrom the low pressure cylinder 6 of the air compressor is passed throughthe bank of coils A and returned to the high pressure cylinder Ill. Theduct l2 from the high pressure cylinder iii connects with the bank ofcoils 28 within the casing i5 so that the second stage of air is passedthrough the bank of coils 8. this air passing out of this bank of coilsB through a duct and into a compressed air storage tank 36 in which thewater or other component which liquifies on cooling collects.

Means are provided for delivering different proportions of outside airfrom the fresh air duct 26 and recirculated or return air from therecirculation air duct 25 into the bottom of the casin i5. For thispurpose a damper 38 is shown as arin the fresh air duct 25 in positionto close the opening from the recirculation air duct 25. Thisrecirculation air damper 38, when moved away from the openin at thelower end of the bypass duct 2b, is also moved to restrict the amount offresh air admitted through the fresh air duct 28, thereby to regulatethe proportion of fresh and recirculated air supplied through theopening 28 into the bottom of the spray chamber within the casing I5.

The mixing damper 38 is shown as being operated by an air motor 39 undercontrol of a thermostat 40 which is shown as immersed in the body ofwater I! at the bottom d'f the spray chamber. The setting of thethermostat is such that when the temperature of the spray watercomprising the body of water I! in which the thermostat 40 is immersedrises above a predetermined temperature, the thermostat 40 actuates thedamper motor 39 to move the damper l8 upwardly toward the proportion offresh air admitted to the spray chamber.

Arranged in the duct 30 is a second damper 45 which is mounted on adamper shaft 46 and so located that it can open the air supply duct 1 tothe compressor either to the fresh air supplied from the lower end ofthe duct 30 or the washed air supplied from the upper end'thereoi. Theposition of this damper is determined by a damper motor 48 which isunder control of a master thermostat 49 and a sub-thermostat 49a. Themaster thermostat is shown as being responsive to the outside airtemperature and the sub-thermostat 49a as being responsive to thetemperature of the air delivered from th spray chamber and thesethermostats are interconnected and actuate the damper motor 48 so thatwhen the outside air temperature is below the temperature of the airdischarged through the exhaust duct 24, the

damper 45 is heldin the dotted line position duct 24, the thermostats 49and 49:: move the damper 45 to the full line position shown in Fig. 2 sothat the cooler and washed air from the exhaust duct 24 is supplied tothe air compressor instead of fresh air.

In the operation of the form of the invention cooling coil B. Afterpassing through the tubes of the cooling coil B the compressed airpasses through a duct to a compressed air tank 36. To provide for theevaporative cooling of the two stages of compressed air so flowingthrough the banks of coils A and B-within the casing IS, the body ofspray water ll in the bottom of the casing is recirculated through theoverhead piping 6 26 admitted to the bottom of the casing. Since therecirculated air from the duct 25 has been humidified on passing thesprays l9 and washed tubes of the banks of cooling coils A andB,increasing the proportion of recirculated airadmitted to the bottom ofthe casing serves to reduce evaporation within the casing l5 and therebyserves to reduce the cooling'efiect upon the streams ofcompressed airpassing through the tubes of the cooling coils A and B. 'Under increasedload conditions, the temperature of the spray water I! will rise and thethermostat 40 actuates the damper motor to lift the damper 38. therebyto decrease the proportion of recirculated air'and increase theproportion of fresh air admitted to the bottom of the casing l5, therebyto increase the cooling effect of the'apparatus and reduce thetemperature of the spray water to the setting of the thermostat 40.

The discharge of the fan housin 20 also connects with the vertical duct30, the lower end of which is open to the atmosphere and the centralpart of which communicates with the duct 1 supplying air to thecompressor. When the temperature of the outside air is higher than thetemperature of the air discharged through the exhaust duct 24, themaster and sub-thermostats 49 and 49a actuate the damper motor 48 tomove the damper to the full line position shown in Fig. 2. In thisposition the air which is supplied to the compressor 5 is the washed airwhich has passed through the casing I5 and since this air is cooler thanthe outside air the efiiciency of the compressor is increased becausethe air from the spray chamber of the evaporative cooler is cooler andheavier than the outside air. When,

have been applied. However, the two banks of I cooling coils'are usedfor cooling the cooling water and air, respectively. and hence have been18 and nozzles l9 so as to wash the tubes of the cooling coils A and Band maintain them in a The discharge 23 of the fan housing 20 connectswith an exhaust duct 24 and also with a recirculation air duct 25 whichis connected with the fresh air inlet duct 26 under control of a damper38. This damper 38 is actuated by the damper motor 39 which in turn isunder control of a thermostat 40 shown as immersed in the spray water H.When the temperature of the spray water drops below the setting of thethermostat 40, the thermostat 40 actuates the damper 38 downwardlythereby to restrict the flow of fresh air into the casing i5 and toincrease the proportion of recirculated air from the recirculation airduct designated as C and D.

The low pressure cylinder 6 of the compressor 5 is shown as suppliedwith air through a duct 1 in the same manner as in the form of theinvention shown in Fig. 1,. but the outlet air duct 50 from the lowpressure cylinder is shown as passing through an intercooler 5i andthence through a duct 52 to the high pressure cylinder Ill of thecompressor. From the high pressure cylinder ill the air passes through aduct 53 into the coil D within the casing l5 of the evaporative heatexchanger and after passing through this coil D the air passes through aduct 54 into a compressedair tank 55 in which'the water or othercomponent which liquifies on cooling collects. The cooling water fromthe low pressure cylinder 6, intercooler 5i and high pressure cylinderl0 passes out through a line 60 into the cooling coil C within thecasing iiand thence is returned by a pump 6i through a line 62 havingbranches connecting with the jackets of the low pressure cylinder 6,intercooler 5i and high pressure cyl-.

inder l0 so that the cooling water is constantly rea a 7 through thecooling coil C and the compressed air is passed through the cooling coilD. Since both of these coils are sprayed with water and also arranged inthe stream of air drawn through the casing l5, it will be seen that boththe cooling water and also the compressed air are cooled in theevaporative heat exchanger in the same manner as with the two stages ofcompressed air in the form of the invention shown in Figs. 1 and In theform of the invention shown in Fig. 4, three banks of coils E, F and Gare arranged in the casing i5 of the evaporative cooler, theconstruction of this evaporative cooler being otherwise identical to theform of the invention shown in Figs. 1 and 2 and hence the samereference numerals having been applied. In the form of the inventionshown in Fig. 4, air is supplied to the low pressure cylinder 6 from aduct 1 as in the form of the invention shown in Figs. 1 and 2 and thisair thence passes through the duct 8 to the cooling coil F in the samemanner as in the form of the invention shown in Figs 1 and 2. Also, aswith the form of the invention shown in Figs. 1 and 2, the air from thecooling coil F passes through a duct II to the high pressure cylinder inand thence through a duct I2 into the cooling coil G from which itpasses through the duct 35 into a compressed air tank 36 in the samemanner as shown in Figs. 1 and 2. Cooling water from the cylinders B andi0 is withdrawn through a line 60 in the same manner as in Fig. 3 and isdrawn through the cooling coil E by a pump 8! and returned to thejackets of the cylinders G and I" through a line 62 in the same manneras shown in Fig. 3. It will be seen that the form of the invention shownin Fig. 4 represents a combination of the forms of the invention shownin Figs. 1-3 and that both stages of air from the compressor and alsothe cooling water of the compressor are separately cooled in the threebanks of coils E, F and G provided in the casing I5 of the evaporativecooler.

All forms of the invention can be used in most sections of the UnitedStates during the summer months to cool the compressed air or gases to alower temperature and having a much lower water content than compressedair or gases cooled by surface water by the best practice. Thus, inmostlocalities of the United States, during the warm weather whencooling is particularlyneeded, the temperature of the surface waterexceeds the average wet bulb temperature by ten or more degrees. Withthis condition and with the ability of cooling the compressed gas orcooling water to within better than 10 F. of this wet bulb temperaturewith the apparatus forming the subject of this invention'as comparedwithcooling the cooling water to 10 F. of the temperature of the surfacewater by shell and tube coolers, it will be seen that by the practice ofthe present invention the air or gas from the comconsequently the watercontent of the compressed air or gas is greatly reduced by the practicsof the present invention. This reduction in the amount of water presentin the compressed air or gas is especially important where thecompressed air or gas is used for operating equipment having rotatingparts and where the water washes out the lubricant of the equipment andsubjects the parts to rapid wear. On release the compressed gas alsoapproaches a freezing temperature and the water in the compressed gastends to freeze and thereby halt production until thawed. In spraypaintin water is especially damaging in that it causes blistering oi thepaint. In blast cleaning equipment where metaliicshot is used, the waterin the compressed air rusts the shot. In many compressed gases, such asilluminating gas and other gases used in the chemical industries, a highwater content is also disadvantageous. By non-condensible gases as usedin the appended claims is meant those gases, such as air, illuminatinggas, or butane, which do not liquify under any normal or usualconditions encountered in the commercial processing or handling of suchgases.

From the foregoing it will be seen that by cooling compressed air or gasin accordance with the present invention, the air or gas is cooled to atemperature of from 10 to 25 F. lower than that which can be obtained bythe best practice with surface water cooling and the air or gas alsocontains only one-half to three-quarters the amount of water. Thereduction of the water content is especially important where thecompressed air or gas is used to drive equipment having rotating parts,where freezing is likely to occur, or where the compressed air is usedin a paint sprayer or in blast cleaning equipment using metallic shot orwhere high water content of the gas is otherwise undesirable.

Further, the present invention provides a single evaporative type ofheat exchanger for cooling a plurality of streams of the cooling wateror compressed gases from a compressor in the same stream of air and bythe same sprays of water. By this means the separate cooling of theseveral streams can be effected in a very compact unit and with aminimum of control instruments. It will also be seen that theevaporative cooler maintains the temperature of the cooling water andgases within very close limits.

We claim as our invention:

1. In combination with a compressor having means for compressing astream of noncondensible gas having a component which liquifles oncooling the compressed gas and a jacket through which a stream ofcooling water is circulated,

means forming a chamber having an air inlet and an air outlet, a fanarranged to force a current of air from said inlet, through said chamberand out through said outlet, a cooling coil arranged inthe current ofair passing through said chamber, means for discharging and distributingwater over, said cooling coil to wet the exterior of said coolin coiland to evaporate and absorb heat therefrom, means for conducting saidstream of non-condensible gas through said cooling coil to cool said gasand liquify said component. and means for collecting said liquifiedcomponent.

2. In combination with a compressor having means for compressing astream of gas and a jacket through which a stream of cooling water iscirculated, means forming a chamber having an air inlet and an airoutlet, a fan arranged to force a current of air from said inlet,through said chamber and out through said outlet. a cooling coilarranged in the current of air passing through said chamber, means fordischarging and distributing water over said cooling coil to wetcharging and distributing water over said cooling coil to wet theexterior of said cooling coil and to evaporate and absorb heattherefrom, means for conducting said stream of non-condensible gas,after compression, through said cooling coil to liquify said component,and means for collecting said liquifled component.

4. In combination with a compressor having means for compressing aplurality of streams of gas and a jacket through which a stream of acooling fluid is circulated, means forming a chamber having an air inletand an air outlet, a fan arranged to force a current of air from saidinlet, through said chamber and out through said outlet, a pair ofindependent cooling coils arranged in the current of air passing throughsaid chamber, means for discharging and distributing water over saidpair of cooling coils to wet the exterior of said cooling coils and toevaporate and absorb heat therefrom, means for continuously conductingone of said streams through one ofsaid pair of cooling coils, and meansfor continuously conducting another of said streams through the other ofsaid pair of cooling coils.

5. In combination with a compressor having means for compressin apluralityof streams of gas having a component which liquefies on coolingthe compressed gas and a jacket through which a stream of a'coolingfluid is circulated,

means forming a chamber having an air inlet and cooling coils arrangedin the current of air passing through said chamber, means fordischarging and distributing water over said pair of cooling coils towet the exterior of said cooling coils and to evaporate and absorb heattherefrom, means for collecting the spent discharged water in saidcasing for recirculation through said discharging and distributingmeans, means for continuously conducting one of said streams through oneof said pair of cooling coils, means for continuouslyconducting anotherof said streams through the other of said pair of cooling coils andmeans for collecting said liquefled component.

6. In combination with a compressor having means for compressing astream of gas and a jacket through which a stream of a cooling fluid iscirculated, means forming a chamber'having coil and to evaporate an airinlet and an air outlet, a fan arranged to force a stream of air fromsaid inlet, through said chamber and out through said outlet, a coolingcoil arranged in the stream of air passing stream of cooling fluidthrough the other the said stream from said compressor passing throughsaid cooling coil, meansfor conducting outside/air to said air inlet, arecirculation air duct conducting a part oi. the stream of air leavingsaid chamber back to said air inlet, and means for adjusting therelative amounts of outside and recirculated air admitted to said airinlet to prevent the temperature of said stream from said compressorfrom falling below a predetermined temperature range, comprising dampermeans in the currents of outside and recirculated air and movable torestrict the flow of one of said currents of air and to relieve therestriction to the flow of the other of said currents of air and viceversa, and thermostat means responsive to the temperature oi one of saidstreams and regulating said dampers.

7. In combination with a compressor having means for compressing aplurality of streams of gas having a component which liquefies oncooling the compressed gas and a jacket through which a stream oi acooling fluid is circulated, means forming a chamber having an air inletand an air outlet, a fan arranged to force a stream of air from saidinlet, through said chamber and out through said outlet, 2. pair ofindependent cooling coils arranged in the stream of air passing throughsaidchamber, means for discharging and distributing a stream of waterover said pair of cooling coils to wet the exterior of said coolingcoils and to evaporate and absorb heat therefrom, means for continuouslyconducting one of the said sti'eams'from said compressor through one ofsaid pair of cooling coils, means for continuously conducting another ofsaid streams from said compressor through the other of said pair ofcooling coils, said streams of air and water normally being heatedthrough heat derived from the said streams from said compressor passingthrough said pair of cooling coils, means for conducting outside air tosaid air inlet,- recirculation air means for conducting a part of thestream of air leaving said chamber back to said air inlet, thermostatmeans responsive to the temperature of-one of said streams to adjust theamount of air so conducted back by said recirculation air means toprevent the temperature of said streams from said compressor fromfalling below a predetermined temperature range and, means forcollecting said liquefied component.

8. In combination with a compressor having means for compressing a gasto provide a stream of compressed gas and a jacket through which astream of cooling fluid is circulated, means forming a chamber having anair inlet'and an air outlet, a fan arranged to force a current of airfrom said inlet, through said chamber and out through said outlet, apair of independent cooling coils arranged in the current of air passingthrough said chamber, means for discharging anddistributing water oversaid pair of cooling coils to wet the exterior of said cooling, coilsand to evaporate and absorb heat therefrom, means forcontinuouslyconducting said stream of compressed gas through one of saidpair of cooling coils, and means for continuously conducting said ofsaid pair of cooling coils. i 9. In combination with a compressor havingmeans for compressing a gas toprovide a stream of compressed gas and ajacket through which a stream of cooling fluid is. circulated, meansforming a chamber having an air inlet and an air outlet; a fan arrangedto force a current of air from said inlet. through said chamber and outand distributing means, means for continuously conducting said stream ofcompressed gas through one of said pair of tooling coils, and means forcontinuously conducting said stream of cooling fluid through the other01 said pair of cooling coils.

10. In combination with a compressor having means for compressing gas toprovide a stream of compressed gas and a jacket through which a streamof cooling fluid is circulated, means forming a chamber having an airinlet and an air outlet, a fan arranged to force a stream of air fromsaid inlet, through said chamber and out through said outlet, a pair ofindependent cooling coils arranged in the stream of air passing throughsaid chamber, means for discharging and distributing a stream of waterover said pair of cooling coils to wet the exterior of said coolingcoils and to evaporate and absorb heat therefrom, means for continuouslyconducting said stream of compressed gas through one of said pair ofcooling coils, means for continuously conducting said stream of coolingfluid through the other of said pair or cooling coils, said streams ofair and water normally being heated through heat derived from thestreams of compressed gas and cooling fluid from said compressor passingthrough said coils, means for conducting outside air to said air inlet,recirculation air means for conducting a part of the stream of airleaving said chamber back to said air inlet, and thermostat meansresponsive to the temperature of one of said streams to adjust theamount of air so conducted back by said recirculation air means toprevent the temperature of said streams of compressed gas and coolingfluid'from said compressor from falling below a. predeterminedtemperature range.

11. In combination with a two stage compressor having means forcompressing as to provide a stream o-i low pressure gas and a stream ofhigh pressure gas, means forming a chamber having an air inlet and anair outlet, a fan arranged to force a stream of air from said inlet,through said chamber and out through said outlet, a pair of independentcooling coils arranged in the current of air passing through saidchambenmeans for discharging and distributing water over said pair ofcooling coils to wet the exterior of said cooling coils and to evaporateand absorb heat therefrom, means for continuously conducting said streamof low pressure gas through one of'said pair of cooling coils and thenceback to said compressor, and means for continuously conducting thestream of high pressure gas through the other of said pair of coolingcoils.

12. In combination with a two stage compressor having means forcompressing gas to provide a stream of low pressure gas and a-stream ofhigh pressure gas, means forming a chamber having an air inlet and anair outlet. a tan arranged to force a stream of air from said inlet,through said chamber and out through said outlet, 9. pair or independentcooling coils arranged in the current of air passing through saidchamber, means for" discharging and distributing water over said pair ofcooling coils to wet the exterior of said cooling coils and to evaporateand absorb heat ther ir m.

means for collecting the spent discharged water in said casing forrecirculation through said discharging and distributing means, means forcontinuously conducting said stream of low pressure gas through one ofsaid pair of cooling coils and thence back to said compressor. and meansfor continuously conducting the stream of high pressure gas through theother of said pair oi cooling coils.

13. In combination with a two stage compressor having means forcompressing gas to provide a stream of low pressure as and a stream ofhigh pressure gas, means forming a chamber having an air inlet and anair outlet, a fan arranged to force a stream of air from said inlet,through said chamber and out through said outlet, a pair of independentcooling coils arranged in the stream of air passing through saidchamber. means for discharging and distributing a stream of water oversaidpair oi coolin coils to wet the exterior of said cooling coils andto evaporate and absorb heat therefrom, means for continuouslyconducting said stream of low pressure gas through one of said pair ofcooling coils and thence back to said compressor, means for continuouslyconductirig the stream of high pressure gas through the other of saidpair of cooling coils, said streams of air and water normally beingheated through heat derived from the streams or gas from said compressorpassing through said coils, means for conducting outside air to said airinlet, recirculation air means for conducting a part of the stream ofair leaving said chamber back to said air inlet, and thermostat meansresponsive to the temperature of one of said streams to adjust theamount of air so conducted back by said recirculation air means toprevent the temperature or said streams of compressed gas from fallingbelow a predetermined temperature range.

14. In combination with a two stage compressor having means forcompressing gas to provide a stream of low pressure gas and a stream ofhigh pressure gas and a jacket through which a stream of cooling fluidis circulated, means forming a chamber having an air inlet and an airoutlet, a fan arranged to force a stream of air from said inlet, throughsaid chamber and out through said outlet, three independent coilsarranged in the current of air passing through said chamber, means fordischarging and distributing water over all of said cooling coils to wetthe exterior of said cooling coils and to evaporate and absorb heattherefrom, means for continuously conducting said stream of low pressuregas through one of said cooling coils and thence back to saidcompressor, means for-continuously conducting said stream of highpressure gas through another of said cooling coils, and means forcontinuously conducting said stream of cooling fluid through the thirdof said coolin coils and thence back to said compressor.

15. In combination with an air compressor having an air inlet and meansfor compressing a stream of air and a jacket through which a stream ofcooling fluid is circulated, means torming a chamber having an airintake and an air outlet, a !an arranged to force a current of air fromsaid air intake, through said chamber and out through said air outlet, acooling coil arranged in the current or air passing through saidchamber, means {or discharging and distributing water over said coolingcoil to wet the exterior of said cooling coil and to evaporate andabsorb heat therefrom, means for continuously conducting one of saidstreams through said cooling coil, and means for conducting the air fromsaid outlot of said casing to said inlet of said compressor.

16. In combination with an air compressor havin an air inlet and meansfor compressing a stream of air and a jacket through which a stream ofcooling fluid is circulated, means forming a chamber having an airintake and an air outlet, :1 fan arranged to force a current of air fromsaid air intake, through said chamber and out through said air outlet. acooling coil arranged in the current of air passing through saidchamber, means for discharging and distributing water over said coolingcoil to wet the exterior of said cooling coil and to evaporate andabsorb heat therefrom, means for continuously conducting ofsaidcompressor, and damper meansror alternately connecting said inleto'fsa'id compressor with-said passages. 1

MARTIN H. OLSTAD. ALLAN-E. WILLIAMS.

M REFERENCES CITED UNITED STATES PATENTS N umber Name Date Reynolds Dec.6, 1910 Richardson Sept. 12, 1922 Buck Sept. 13, 1932 Coverston Mar. 23,1937 Noble Mar. 23, 1937 Cook May 31, 1938 Laird Aug. 9, 1938 Coey June13, 1939 Strang Nov. 12,-1940 Mollenberg Mar, 4, 1941 Chapman Mar.31,1942

